commit 30e41798f40c684be57d7ccfebf5c6ad94c0ff97

Author: Petr Viktorin <pviktori@redhat.com>

Date:   Wed Jan 20 15:21:43 2021 +0100

    CVE-2021-3177: Replace snprintf with Python unicode formatting in ctypes param reprs

    Backport of Python3 commit 916610ef90a0d0761f08747f7b0905541f0977c7:

    https://bugs.python.org/issue42938

    https://github.com/python/cpython/pull/24239

diff --git a/Lib/ctypes/test/test_parameters.py b/Lib/ctypes/test/test_parameters.py

index 23c1b6e2259..77300d71ae1 100644

--- a/Lib/ctypes/test/test_parameters.py

+++ b/Lib/ctypes/test/test_parameters.py

@@ -206,6 +206,49 @@ class SimpleTypesTestCase(unittest.TestCase):

         with self.assertRaises(ZeroDivisionError):

             WorseStruct().__setstate__({}, b'foo')

+    def test_parameter_repr(self):

+        from ctypes import (

+            c_bool,

+            c_char,

+            c_wchar,

+            c_byte,

+            c_ubyte,

+            c_short,

+            c_ushort,

+            c_int,

+            c_uint,

+            c_long,

+            c_ulong,

+            c_longlong,

+            c_ulonglong,

+            c_float,

+            c_double,

+            c_longdouble,

+            c_char_p,

+            c_wchar_p,

+            c_void_p,

+        )

+        self.assertRegexpMatches(repr(c_bool.from_param(True)), r"^<cparam '\?' at 0x[A-Fa-f0-9]+>$")

+        self.assertEqual(repr(c_char.from_param('a')), "<cparam 'c' ('a')>")

+        self.assertRegexpMatches(repr(c_wchar.from_param('a')), r"^<cparam 'u' at 0x[A-Fa-f0-9]+>$")

+        self.assertEqual(repr(c_byte.from_param(98)), "<cparam 'b' (98)>")

+        self.assertEqual(repr(c_ubyte.from_param(98)), "<cparam 'B' (98)>")

+        self.assertEqual(repr(c_short.from_param(511)), "<cparam 'h' (511)>")

+        self.assertEqual(repr(c_ushort.from_param(511)), "<cparam 'H' (511)>")

+        self.assertRegexpMatches(repr(c_int.from_param(20000)), r"^<cparam '[li]' \(20000\)>$")

+        self.assertRegexpMatches(repr(c_uint.from_param(20000)), r"^<cparam '[LI]' \(20000\)>$")

+        self.assertRegexpMatches(repr(c_long.from_param(20000)), r"^<cparam '[li]' \(20000\)>$")

+        self.assertRegexpMatches(repr(c_ulong.from_param(20000)), r"^<cparam '[LI]' \(20000\)>$")

+        self.assertRegexpMatches(repr(c_longlong.from_param(20000)), r"^<cparam '[liq]' \(20000\)>$")

+        self.assertRegexpMatches(repr(c_ulonglong.from_param(20000)), r"^<cparam '[LIQ]' \(20000\)>$")

+        self.assertEqual(repr(c_float.from_param(1.5)), "<cparam 'f' (1.5)>")

+        self.assertEqual(repr(c_double.from_param(1.5)), "<cparam 'd' (1.5)>")

+        self.assertEqual(repr(c_double.from_param(1e300)), "<cparam 'd' (1e+300)>")

+        self.assertRegexpMatches(repr(c_longdouble.from_param(1.5)), r"^<cparam ('d' \(1.5\)|'g' at 0x[A-Fa-f0-9]+)>$")

+        self.assertRegexpMatches(repr(c_char_p.from_param(b'hihi')), "^<cparam 'z' \(0x[A-Fa-f0-9]+\)>$")

+        self.assertRegexpMatches(repr(c_wchar_p.from_param('hihi')), "^<cparam 'Z' \(0x[A-Fa-f0-9]+\)>$")

+        self.assertRegexpMatches(repr(c_void_p.from_param(0x12)), r"^<cparam 'P' \(0x0*12\)>$")

+

 ################################################################

 if __name__ == '__main__':

diff --git a/Misc/NEWS.d/next/Security/2021-01-18-09-27-31.bpo-42938.4Zn4Mp.rst b/Misc/NEWS.d/next/Security/2021-01-18-09-27-31.bpo-42938.4Zn4Mp.rst

new file mode 100644

index 00000000000..7df65a156fe

--- /dev/null

+++ b/Misc/NEWS.d/next/Security/2021-01-18-09-27-31.bpo-42938.4Zn4Mp.rst

@@ -0,0 +1,2 @@

+Avoid static buffers when computing the repr of :class:`ctypes.c_double` and

+:class:`ctypes.c_longdouble` values.

diff --git a/Modules/_ctypes/callproc.c b/Modules/_ctypes/callproc.c

index 066fefc0cca..5cc3c4cf685 100644

--- a/Modules/_ctypes/callproc.c

+++ b/Modules/_ctypes/callproc.c

@@ -460,50 +460,62 @@ PyCArg_dealloc(PyCArgObject *self)

 static PyObject *

 PyCArg_repr(PyCArgObject *self)

 {

-    char buffer[256];

     switch(self->tag) {

     case 'b':

     case 'B':

-        sprintf(buffer, "<cparam '%c' (%d)>",

+        return PyString_FromFormat("<cparam '%c' (%d)>",

             self->tag, self->value.b);

-        break;

     case 'h':

     case 'H':

-        sprintf(buffer, "<cparam '%c' (%d)>",

+        return PyString_FromFormat("<cparam '%c' (%d)>",

             self->tag, self->value.h);

-        break;

     case 'i':

     case 'I':

-        sprintf(buffer, "<cparam '%c' (%d)>",

+        return PyString_FromFormat("<cparam '%c' (%d)>",

             self->tag, self->value.i);

-        break;

     case 'l':

     case 'L':

-        sprintf(buffer, "<cparam '%c' (%ld)>",

+        return PyString_FromFormat("<cparam '%c' (%ld)>",

             self->tag, self->value.l);

-        break;

 #ifdef HAVE_LONG_LONG

     case 'q':

     case 'Q':

-        sprintf(buffer,

-            "<cparam '%c' (%" PY_FORMAT_LONG_LONG "d)>",

+        return PyString_FromFormat("<cparam '%c' (%lld)>",

             self->tag, self->value.q);

-        break;

 #endif

     case 'd':

-        sprintf(buffer, "<cparam '%c' (%f)>",

-            self->tag, self->value.d);

-        break;

-    case 'f':

-        sprintf(buffer, "<cparam '%c' (%f)>",

-            self->tag, self->value.f);

-        break;

-

+    case 'f': {

+        PyObject *s = PyString_FromFormat("<cparam '%c' (", self->tag);

+        if (s == NULL) {

+            return NULL;

+        }

+        PyObject *f = PyFloat_FromDouble((self->tag == 'f') ? self->value.f : self->value.d);

+        if (f == NULL) {

+            Py_DECREF(s);

+            return NULL;

+        }

+        PyObject *r = PyObject_Repr(f);

+        Py_DECREF(f);

+        if (r == NULL) {

+            Py_DECREF(s);

+            return NULL;

+        }

+        PyString_ConcatAndDel(&s, r);

+        if (s == NULL) {

+            return NULL;

+        }

+        r = PyString_FromString(")>");

+        if (r == NULL) {

+            Py_DECREF(s);

+            return NULL;

+        }

+        PyString_ConcatAndDel(&s, r);

+        return s;

+    }

     case 'c':

-        sprintf(buffer, "<cparam '%c' (%c)>",

+        return PyString_FromFormat("<cparam '%c' ('%c')>",

             self->tag, self->value.c);

-        break;

 /* Hm, are these 'z' and 'Z' codes useful at all?

    Shouldn't they be replaced by the functionality of c_string

@@ -512,16 +524,13 @@ PyCArg_repr(PyCArgObject *self)

     case 'z':

     case 'Z':

     case 'P':

-        sprintf(buffer, "<cparam '%c' (%p)>",

+        return PyUnicode_FromFormat("<cparam '%c' (%p)>",

             self->tag, self->value.p);

-        break;

     default:

-        sprintf(buffer, "<cparam '%c' at %p>",

-            self->tag, self);

-        break;

+        return PyString_FromFormat("<cparam '%c' at %p>",

+            (unsigned char)self->tag, (void *)self);

     }

-    return PyString_FromString(buffer);

 }

 static PyMemberDef PyCArgType_members[] = {